Suitability of six lymnaeid snails for infection with Fasciola hepatica

The suitability of Fossaria (Bakerilymnaea) cubensis and Pseudosuccinea columella from Louisiana as intermediate hosts for Fasciola hepatica was compared to P. columella and Stagnicola elodes from Ann Arbor, MI, S. attenuata from Hidalgo, Mexico, Lymnaea gedrosiana from Iran and L. natalensis from Senegal. P. columella from LA was shown to be a more suitable host (51.3% became infected) than F. (B.) cubensis (15.2% and 26.4% of two populations became infected). The infection rate for P. columella from MI, was 50% and for L. gedrosiana was 32.5%, whereas L. natalensis, S. elodes and S. attenuata were refractory. F. (B.) cubensis and P. columella have some degree of suitability as intermediate hosts for F. hepatica under laboratory conditions, but field observations of their habitat in southern LA and characteristic management of cattle indicate that the former snail is more important as an intermediate host in this enzootic area. Tissue sections of suitable snails had few histopathological effects but physical damage caused by rediae was pronounced, mainly in the digestive gland and in the mantle.     

Survival of snails and characteristic lesions of Fasciola hepatica infection in four European species of Lymnaea.

The survival of snails and characteristic organ lesions were investigated in four different age categories (new-born, 1 and 2 mm shell height, adults) and in four species of Lymnaea (L. glabra, L. palustris, L. peregra ovata, L. truncatula) infected by Fasciola hepatica. Mortalities were higher in infected groups on Days 30 and 45 post-infection (+42% and +45%, respectively) than in controls. Lesions depended on the species and age of the Lymnaea. Epithelial necrosis of the kidney was recorded in L. glabra, L. palustris and L. p. ovata, whereas intralamellar deposits were found in the same organ of L. truncatula. All categories of L. truncatula had evolutive infections (snails with living parthenitae); the young snails of other species became infected, but the adults did not, as estimated at Day 45 post-infection. The lesions were related to the intensity of evolutive infections: necrosis of the digestive gland was found in moderate to low infections and, conversely, gonadal atrophy with epithelial necrosis was found in highly infected snails.     

PCR diagnosis of Fasciola hepatica in field-collected Lymnaea columella and Lymnaea viatrix snails

Fasciolosis, caused by the trematode Fasciola hepatica, is a zoonosis of economic importance in livestock that is emerging as a chronic disease in humans. The intermediate hosts are lymnaeid snails, in which diagnosis of infection is traditionally based on cercarial shedding, tissue sectioning and crushing. We developed a PCR assay for the sensitive and specific detection of F. hepatica in field-collected Lymnaea sp. snails. A primer pair was designed to amplify a 405 bp fragment of the cytochrome c oxidase subunit 1 gene of F. hepatica. The PCR assay showed a limit of detection of 10 pg of genomic F. hepatica DNA. No cross-reactions were observed with samples from other related trematode species or from the snail hosts Lymnaea columella and Lymnaea viatrix. DNA sequencing of the amplicon showed 100% homology with F. hepatica, and 75-89% homology with other trematodes on regions that did not include the entire set of primers. Two samples from Argentina were analysed. For snails in sample 1 (n = 240), identified as L. columella, the infection rate was 17.5 and 51.3% by direct examination and PCR, respectively. For snails in sample 2 (n = 34), identified as L. viatrix, the infection rate was 2.9 and 61.8% by direct examination and PCR, respectively. Differences in infection rates between these diagnosis methods were significant for both samples. Our PCR technique showed to be effective for detecting specific F. hepatica infections of low intensity in the intermediate host, and hence it could be used to study the epidemiological situation in a given area, as well as to assess host suitability for the parasite.     

The effect of pre-exposure to Fasciola hepatica or Schistosoma mansoni on challenge infection with Fasciola hepatica

Two groups of 12 and 6 rats were inoculated with Fasciola hepatica and Schistosoma mansoni, respectively. The Schistosoma-inoculated group, as well as 6 Fasciola-inoculated rats and 6 uninfected rats were challenged 8 weeks later with F. hepatica. A control group of 6 rats was left unexposed. Eight weeks after the challenge exposure all rats were necropsied and subjected to post-mortem examination. The number of Fasciola recovered after challenge was lower in both groups of rats primarily infected with F. hepatica or S. mansoni. F. hepatica-induced pathological changes were observed in all infected rats, but were pronounced in the group which was first exposed at the time of challenge of the primarily infected groups. No Schistosoma eggs or adults were detected in Schistosoma-inoculated rats. The results demonstrated that rats primarily infected with F. hepatica acquired resistance against a challenge exposure to the homologous parasite. Also S. mansoni, even without patency, can provide partial protection against F. hepatica infection.     

Chemotherapy of infection with Fasciola hepatica in cattle.

Diamphenethide and a mixture of nitroxynil and hexachlorophane, which are effective against Fasciola hepatica in sheep, are effective in cattle if allowance is made for the slower rate of development and the more intense liver reaction which is associated with resistance. Adult parasites are mostly rejected around the time of maturity so that therapy in cattle must be directed against the early developmental stage using an appropriate drug.     

Treatment of Fasciola hepatica infection in horses with triclabendazole

Thirteen thoroughbred foals with an adult infection and a presumed immature infection with Fasciola hepatica were treated with 12 mg triclabendazole/kg bodyweight. The absence of eggs from samples of faeces examined at intervals up to 110 days after treatment showed that all the animals were cured. In a second trial the same dose of triclabendazole cured 11 of 12 foals whereas nitroxynil at 7 mg/kg cured only six of 12 foals. No side effects were observed after treatment.     

Response of sheep to challenge infection with Fasciola hepatica

Sheep were infected with 100 metacercariae of Fasciola hepatica and reinfected 16 weeks later with a further 100 metacercariae. Serum samples were taken weekly for 36 weeks after primary infection. Serum was assayed for the presence of the enzymes glutamate dehydrogenase (GLDH) and gamma-glutamyl transferase (gamma-GT), as indicators of liver and bile duct damage respectively, and for levels of precipitating antibody. Antibody and GLDH levels rose following the primary infection but fell after patency had been reached . A peak in gamma-GT activity was associated with the onset of patency. After the challenge infection levels of both enzymes rose substantially and there were persistent fluctuations in activity. Antibody levels did not rise markedly following challenge but fluctuated at low levels until autopsy, 20 weeks after challenge. There was no resistance to challenge judged by worm recoveries at autopsy. It is suggested that the presence of adult flukes in the bile ducts suppresses the antibody response to challenge infection. Tissue damage, which is shown by fluctuations in GLDH and gamma-GT levels after adult flukes have become established in the bile ducts, is considered to be due to the feeding activity of adult flukes and the deposition of immune complexes in the liver parenchyma.     

Fasciola hepatica infection in farmed emus (Dromaius novaehollandiae)

Objective To describe two cases of infection with Fasciola hepatica i n young farmed emus, subacute and chronic fasci-olosis and a response to treatment of the flock with albenda-zole.
Procedure Gross lesions were found at necropsy and hepatic lesions in microscopic examination. The parasite recovered from one emu was identified by its morphological characteristics and an egg count reduction test was carried out after treatment of the flock with albendazole.
Results Hepatic lesions resembling subacute and chronic fasciolosis of ruminants were identified. An adult fluke was recovered from the liver of one of the birds and was identified as F hepatica . The eggs of the fluke were irregular in shape and size. No fluke eggs were identifiable in faeces of live emus 10 days after treatment of the flock with albendazole at a dose of 10 mg/kg.
Conclusions This is the first reported case of infection with F hepatica i n farmed emus and the first report of the occurrence of Fasciola infection is the class Aves. The irregular shape and size of the eggs may be attributable to infection of an aberrant host. Treatment with albendazole eliminated eggs from the faeces of the flock.     

Dynamics of Fasciola hepatica transmission in the Andean Patagonian valleys, Argentina

We described the transmission dynamics of Fasciola hepatica at its southern distribution range. Studies of prevalence and egg output in cattle and population dynamics and infection in snails were performed in a farm in the Andean Patagonian valleys, Argentina, between December 1998 and February 2002. Snail surveys were conducted from spring to autumn. Infection was diagnosed coprologically in the whole herd at the beginning and end of the study, and in a cohort of heifers at the beginning and end of 2001. A twice-a-year anthelmintic treatment was implemented in 1999. The relationship of the variables mentioned above with temperature and rainfall was determined. Lymnaea viatrix showed a life-span of about 15 months and an annual pattern of population dynamics. Specimens were frequently found in temporary environments and lagoons, and rarely in streams. Snail abundance and soil-water availability were directly related in temporary environments and inversely related in lagoons. Overall prevalence in L. viatrix was 0.67% (range: 0.9-14%) and infection was detected in summer and autumn. At the beginning of the study, calves were the least infected age group (15%). Prevalences and median egg counts in grazing animals were similar at the beginning (heifers: 81%, 3.3 epg; cows: 60%, 1.3 epg) and end of the study (heifers and cows: around 51%, 1 epg). Likewise, the prevalence in the cohort of heifers remained similar (around 40%) between surveys. Transmission to cattle was highly effective despite of the short activity period and the low infection rate of snails, and the regular anthelminthic treatment. There would be two seasonal transmission peaks, one in summer-autumn, when infected snails were present, and the other in early spring due to overwintering metacercariae. Some recommendations based on the climatic conditions of the region are provided to minimize snail infection and ultimately to reduce the incidence of fasciolosis in cattle.     

Detection of Fasciola gigantica infection in snails by polymerase chain reaction

Polymerase chain reaction (PCR) was used to detect Fasciola gigantica infection in the snail intermediate host. Fasciola specific primers amplified a 124 bp fragment in PCR when the genomic DNA isolated from F. gigantica infected Lymnaea auricularia snails was used as template. In addition to the 124 bp amplicon, a ladder of DNA fragments representing amplification of the 124 bp repetitive sequences was observed. Genomic DNA of the parasite was used as a positive control, which also gave an amplification of the 124 bp fragment. DNA isolated from non-infected snails was used as a negative control and no amplification of this sequence was observed. This technique is highly specific and sensitive and possesses fairly good prospects of its utility as an epidemiological tool for ascertaining the infectivity status in ubiquitous snail populations.     

Responses of Fasciola hepatica infected sheep to various infection levels

The response to Fasciola hepatica was studied in sheep infected with 5, 30, 150 metacercariae. The animals were necropsied 12 weeks post-infection (p-i) for counting and measuring flukes. Cellular and humoral responses were detected by peripheral eosinophil count, peripheral blood lymphocyte proliferation with excretory-secretory products (FhESP) and ELISA. All sheep were infected at necropsy except one sheep which was infected with 5 metacercariae. Mean parasitic intensities were 40%, 44% and 27% of the infection dose in sheep infected with 5, 30, 150 metacercariae respectively. FhESP-specific lymphocyte responses of the 3 infected groups were significantly enhanced in weeks 3 and 4 p-i (p < 0.05). The kinetics of the specific humoral response were similar for the 3 infected groups but the antibody level was significantly lower in animals infected with 5 metacercariae than in the 2 other infected groups from week 5 p-i to week 12 p-i (p < 0.05). Peripheral eosinophil count was significantly enhanced (p < 0.05) in infected groups. The numbers of peripheral eosinophils were significantly different between the 3 infected groups in week 3, 4 and 6 p-i and were related to infection level. These results confirm that sheep are highly susceptible to F. hepatica infection, even when infection pressure is very low. Peripheral eosinophilia was dependent of the infection level. The immune response was similar in sheep infected with various numbers of flukes.     

湖南岳阳市耕牛肝片吸虫感染情况调查

共调查待宰的耕牛300头，发现肝片吸虫的虫体感染率和虫卵阳性率分别为38．67％，69．00％。另外还发现，不同区域、不同种、不同年龄等因素对肝片吸虫的感染率均有较大影响。